In a future wireless network, a high throughput can be achieved in two manners. In one manner, a large quantity of multiple-input multiple-output (MIMO) antennas are used. The other is ultra-dense network deployment. The large quantity of MIMO antennas is a large quantity of antennas used at a base station, and MIMO performance easily leads to system capacity saturation due to space limitation. In an ultra-dense network, deployment costs of a micro base station are less than those of a macro base station, and an optimal connection can be achieved by means of an intelligent handover. In a long-distance location, only a micro base station needs to be deployed, while a macro base station with many antennas does not need to be deployed. A micro base station supports a plurality of radio technologies, but delivers handover performance inferior to that of a macro base station. In particular, in a mobile network in which a macro base station and a micro base station are deployed in a mixed way, mobility management for user equipment (UE) is more complex.
In such a mobile network with mixed deployment, the mobile network has an enormous size and is complex, and handovers between cells become increasingly important in device mobility management and performance analysis. Currently, as mobile networks develop, service types are diversified, and mobility complexity of user equipment grows. Consequently, a prior mechanism for handovers between cells cannot adapt to a complex network environment well.
In a handover process in a Long Term Evolution (LTE) system, there are five procedures on a control plane: measurement, measurement reporting, handover preparation, handover command, and handover completion. In the handover command and handover completion procedures, data transmission over an air interface is interrupted when a terminal is handed over from a source base station to a new target base station. Therefore, it is necessary to make handover improvement, to reduce control plane handover latency and user plane data interruption. In the handover process, the foregoing five procedures need to be performed on the control plane to complete a handover. In the handover command and handover completion procedures, however, the terminal breaks a connection to a source cell and connects to a target cell. Therefore, data transmission is interrupted in these procedures.
In the prior art, the following several handover improvement methods are used to reduce control plane handover latency and user plane data interruption. In one handover improvement method, a pre-handover method is used. Compared with the foregoing normal handover, with a handover preparation made on a possible target cell before a handover, a handover preparation procedure may no longer be required after an actual measurement report triggers a handover, and a source cell directly sends a handover command for the prepared handover target cell to the terminal. Therefore, control plane latency is shortened in a handover process. However, the terminal still needs to connect to the target cell after being disconnected from the source cell; therefore, data transmission interruption is still present in the handover process.
To further shorten the handover process, there is still the following handover improvement method in the prior art: Based on the pre-handover method, a handover process is initiated by a terminal instead of a network; therefore, on the control plane, when a terminal determines to perform a handover, the terminal is directly handed over to a prepared target cell to complete a handover process. Because user-plane data needs to be forwarded to the target cell from the source cell, data interruption is also present in the case of this method. The data interruption is not relieved until a data stream is forwarded to the target cell, after the terminal handover is completed and the target cell requests the source cell or a data forwarding node to forward the data stream.
To overcome the data interruption problem in the foregoing method, there is still the following handover improvement method in the prior art: A plurality of connections are established between a terminal and a plurality of cells, and the terminal does not break a connection to a source cell before accessing a target cell; therefore, the terminal may still continue to communicate with the source cell before being connected to the target cell, until subsequent data transmission is gradually switched to the target cell. Theoretically, the data interruption problem can be eliminated completely by using this method.
However, in the foregoing handover improvement solution, the method of establishing a plurality of connections can avoid data interruption, but the terminal still needs to identify the target cell as early as possible and add, by using signaling, the target cell to a multi-connection cell set, and needs to update the set continually, so that a plurality of connected cells may be used for multi-connection transmission at any time. When cells are deployed densely, there may be several or even tens of cells surrounding the terminal. Therefore, the prior art is subject to a problem of relatively high cell management and maintenance costs. In addition, frequent cell addition or deletion may not cause a call drop, but may greatly affect an effective transmission rate. As perceived by a user, a signal is always good, but a transmission rate is unstable, and data transmission efficiency is quite low.